Removable Membrane Having a Truncated Tab

ABSTRACT

A removable membrane, or cover, for a disposable food container includes a membrane portion at least partially defined by a circular outer perimeter edge. The removable membrane further includes a truncated tab portion projecting radially outward of the outer perimeter edge of the membrane portion. The truncated tab portion is at least partially defined by a first lateral edge and a second lateral edge, with each of the first and second lateral edges converging as the tab portion extends away from the outer perimeter edge of the membrane portion. The tab portion is further defined by a forward edge that extends along a straight line between the first lateral edge and second lateral edge, wherein the forward edge is disposed at an oblique angle relative to the first lateral edge and the second lateral edge.

FIELD OF THE DISCLOSURE

This disclosure relates generally to containers and, more particularly, to removable membranes for covering containers.

BACKGROUND

Disposable food containers are commonly used to store food products, such as individual-sized portions of yogurt or fruit, for example. As illustrated in FIG. 1A, the typical disposable food container 10 has a removable membrane 12 that acts as a cover for the disposable food container 10, and the removable membrane 12 may be applied in an automated process that seals the disposable food container 10. In such an automated process, a stack of membranes 12 are typically retained in a magazine 14 (shown in FIG. 1B), which includes a number of vertical rods 16 that collectively maintain the membranes 12 in mutual alignment in a manner that will be described in more detail below. As containers 10 pass adjacent to the magazine 14 on a conveyor, for example, a grabber or suction device removes a single membrane 12 from the magazine 14 and place the same on a passing container 10, which has previously been filled with product (e.g., yogurt, cheese, fruit, etc.). A lid (not shown), which may be stored in a separate magazine 14 from the magazine containing the stack of membranes 12, may then be placed on the passing container 10 over the membrane 12 to provide additional protection to the container 10.

The removable membrane 12 is typically made of an impermeable foil or film material that is secured by an adhesive, which may be a heat sealable coating or film, to a flange portion 14 formed around the upper circumference of the container 10. The removable membrane 12 is typically sized and shaped to correspond to the perimeter of the flange portion 18 of the container 10. Generally, this shape is circular, but the perimeter of the flange portion (and the shape of the container 10 itself) may have any shape, such as that of a triangle, an oval, or a square, for example. On known removable membranes, a rounded triangular tab portion 20 may project radially outward of the outer perimeter of the flange portion 18 of the container 10, as illustrated in FIG. 2. However, the flange portion 18 in the vicinity of the rounded triangular tab portion 20 may radially extend away from a center portion of the container to correspond in shape to the rounded triangular tab portion 20. Typically, the rounded tab portion 20 is defined by a first lateral edge 22 and a second lateral edge 24, with each of the first and second lateral edges 22, 24 converging as the rounded tab portion extends away from the outer perimeter of the flange portion 18. The rounded tab portion 20 is further defined by a front edge 26 that extends between the first lateral edge 22 and the second lateral edge 24. The front edge 26 may be semi-circular in shape, and the semi-circle may tangentially intersect each of the first lateral edge 22 and the second lateral edge 24, as illustrated in FIG. 1B.

The conventional rounded triangular design of the tab portion 20 has several disadvantages. For example, the conventional tab portion 20 is large in relation to the membrane portion 12, and the relatively large tab portion 20 increases material costs. The relatively large tab portion 20 also detracts from the visual appeal of the packaging of the container 10. In addition, the large tab portion 20 may interfere with secondary packaging such as shrink-wrap, cardboard sleeves, etc. For example, the large tab portion 20 may extend beyond the perimeter of a cardboard sleeve or multipack, and the large tab portion 20 may adversely interact with secondary packaging.

Other embodiments of known removable membranes may include a relatively smaller rounded tab portion 20 than the conventional rounded triangular design. For example, such an embodiment may include a rounded tab portion 20, as depicted in FIG. 1C, defined by a first lateral edge 22 and a second lateral edge 24 that are mutually-parallel, and a front edge 26 that is a semi-circular arc. In a further embodiment of a known removable membrane 12 shown in FIG. 1D, a single semi-circular edge 26 may completely define the rounded tab portion 20. However, these embodiments suffer from several drawbacks. Importantly, these embodiments may not be usable in conventional magazines 14 such as those consisting of a plurality of rods 16, as shown in FIG. 1B, because the first lateral edge 22 and a second lateral edge 24 in the embodiment shown in FIG. 1C (and the a single semi-circular edge 26 of the embodiment shown in FIG. 1D) do not engage the vertical rods 16 that are positioned adjacent to the tab portion 20. Because the first lateral edge 22 and a second lateral edge 24 of the embodiment shown in FIG. 1C (and the a single semi-circular edge 26 of the embodiment shown in FIG. 1D) do not engage vertical rods 16, the removable membranes 12 stacked in the magazine 14 would rotate relative to other removable membranes 12, thereby resulting in misfeeds and jams during use.

BRIEF SUMMARY OF THE DISCLOSURE

In accordance with one exemplary aspect of the present invention, a removable membrane for a disposable food container includes a membrane portion being at least partially defined by a circular outer perimeter edge. The removable membrane further includes a truncated tab portion projecting radially outward of the outer perimeter edge of the membrane portion. The truncated tab portion is at least partially defined by a first lateral edge and a second lateral edge, with each of the first and second lateral edges converging as the tab portion extends away from the outer perimeter edge of the membrane portion. The tab portion is further defined by a forward edge that extends along a straight line between the first lateral edge and second lateral edge, wherein the forward is disposed at an oblique angle relative to the first lateral edge and the second lateral edge.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an known embodiment of a food container having a removable membrane for a cover;

FIG. 1B is a top view of an known embodiment of a removable membrane showing a plurality of vertical rods of a magazine;

FIG. 1C is a top view of a further known embodiment of a removable membrane;

FIG. 1D is a top view of a still further known embodiment of a removable membrane;

FIG. 2A is a top view of an embodiment of a removable membrane constructed in accordance with the present disclosure showing a plurality of vertical rods of a magazine;

FIG. 2B is a partial top view of a further embodiment of a removable membrane constructed in accordance with the present disclosure with the vertical rods of the magazine omitted for clarity;

FIG. 3A is atop view of a still further embodiment of a removable membrane constructed in accordance with the present disclosure with the vertical rods of the magazine omitted for clarity;

FIG. 3B is a partial top view of another embodiment of a removable membrane constructed in accordance with the present disclosure with the vertical rods of the magazine omitted for clarity;

FIG. 4A is a partial top view of still another embodiment of a removable membrane constructed in accordance with the present disclosure with the vertical rods of the magazine omitted for clarity; and

FIG. 4B is a partial top view of a further embodiment of a removable membrane constructed in accordance with the present disclosure with the vertical rods of the magazine omitted for clarity.

DETAILED DESCRIPTION

FIGS. 2A to 4B illustrate a removable membrane 28 constructed in accordance with the present disclosure, and which includes a membrane portion 30 and a truncated tab portion 32. As shown in FIG. 2A, the membrane portion 30 is at least partially defined by an outer perimeter edge 34. The truncated tab portion 32 is at least partially defined by a first lateral edge 36, a second lateral edge 38, and a forward edge 40 that extends between the first lateral edge 36 and the second lateral edge 38. The forward edge 40 may have the shape of a linear segment or an arc, for example. The first lateral edge 36, the second lateral edge 38, and the forward edge 40 may collectively take the shape of a truncated triangle. Said another way, the membrane portion 30 and the truncated tab portion 32 may generally have the shape of a teardrop having a flat or relatively flat forward edge 40. So configured, each removable membrane 28 may require less material than conventional removable membranes, and the truncated tab design reduces the distance that the tab portion 32 radially extends away from the membrane portion 30, thereby minimizing the damage or undesirable interaction with the secondary packaging of adjacent item. Furthermore, a stack of the removable membranes 12 may be stored in conventional magazines 14 without the need to modify or in any way reconfigure the magazine 14.

Referring to FIG. 2A and as mentioned, the removable membrane 28 of the present example has a membrane portion 30. The membrane portion 30 may be defined by the outer perimeter edge 34 that may correspond in shape to the outer perimeter 42 of a flange portion 18 of the container 10. For example, the outer perimeter edge 34 of the embodiment illustrated in FIG. 2A has a generally circular shape. Such a circular outer perimeter edge 34 may have any suitable diameter, such as, for example, 79 mm. In alternate embodiments, the outer perimeter edge 34 may have the shape of a triangle, an oval, a square, or any other appropriate shape that may correspond to the particular shape of the perimeter of the flange portion of a particular container 10.

Still referring to FIG. 2A, the removable membrane 28 also includes a truncated tab portion 32 that may project radially outward of the outer perimeter edge 34 of the membrane portion 30. Said another way, the truncated tab portion 32 that may project radially outward of the outer perimeter 42 of the flange portion 18 of the container 10 when the removable membrane 28 is secured to a food container 10. The membrane portion 30 and the truncated tab portion 32 may be formed from a single piece of material in a die-cutting operation. Therefore, it can be said that the removable membrane 28 constitutes a flat, planar sheet of material that is solid (e.g., non-perforated) and capable of providing an air-tight seal to a food container or other container, as desired. More specifically, the material may be an impermeable foil or film, such as PET, paper/foil/film composites, or paper/film composites, for example. The truncated tab portion 32 may be defined by a first lateral edge 36 and a second lateral edge 38, with each of the first and second lateral edges 36, 38 converging as the truncated tab portion 32 extends away from the outer perimeter edge 34 of the membrane portion 30 (i.e., as the truncated tab portion 32 extends away from the outer perimeter 42 of the flange portion 18 when the removable membrane 28 is secured to a food container 10). More specifically, each of the first and second lateral edges 36, 38 may converge towards a tab axis 44 that bisects the truncated tab portion 32 and extends through a center point of the circular membrane portion 30, and each of the first and second lateral edges 36, 38 may form an angle α between about 35 degrees and about 55 degrees with the tab axis 44. For example, each of the first and second lateral edges 28, 30 may form an angle α of about 45 degrees with the tab axis 44. As illustrated in FIG. 2A, each of the first and second lateral edges 28, 30 may be symmetrically disposed about the tab axis 44. However, in alternate examples, the first lateral edge 36 and the second lateral edge 38 may be asymmetrically disposed about the tab axis 44. In still other alternate examples, the first lateral edge 36 and the second lateral edge 38 may not converge, but instead may be parallel.

As illustrated in FIG. 2A, the first lateral edge 36 and second lateral edge 38 may each be a single linear segment. However, the first lateral edge 36 and second lateral edge 38 may have any desired shape, and each may include one or more linear segments and/or one or more curved segments, for example. Referring again to FIG. 2A, the first lateral edge 36 and second lateral edge 38 may tangentially intersect the outer perimeter edge 34 of the membrane portion 30. However, the first lateral edge 36 and the second lateral edge 38 may intersect the outer perimeter edge 34 of the membrane portion 30 at any appropriate angle.

Still referring to FIGS. 2A and 2B, the truncated tab portion 32 may be further defined by a forward edge 40 that extends between the first lateral edge 36 and the second lateral edge 38. The forward edge 40 may extend along a straight line L (shown in FIG. 2A) between the first lateral edge 36 and the second lateral edge 38 such that the forward edge 40 is a linear segment 46, and the linear segment 46 may be bisected by the tab axis 44. The linear segment 46 may intersect each of the first and second lateral edges 36, 38 to form an oblique angle β such that the truncated tab portion 32 has the shape of a truncated triangle, as illustrated in FIG. 2A. Put another way, the linear segment 46, the first lateral edge 36 and the second lateral edge 38 may collectively have the general shape of an upper portion (e.g., the upper three sides) of a trapezoid. More specifically, the linear segment 46, the first lateral edge 36, and the second lateral edge 38 may each correspond to a top side, an inwardly tapering first lateral side, and an inwardly tapering second lateral side, respectively, of a trapezoid that is wider at the base (i.e., a reference line that is parallel or substantially parallel to the linear segment 46 and that extends between the first and second lateral edges 36, 38) and tapers towards the top (i.e., the linear segment 46). In an example of the removable membrane 28, the linear segment 46 may form an angle β between about 115 degrees and about 155 degrees with the first lateral edge 36 and the second lateral edge 38. More specifically, the linear segment 46 may form an angle of 135 degrees (or approximately 135 degrees) with the first lateral edge 36 and the second lateral edge 38.

As illustrated in FIG. 2A, the forward edge 40 and the outer perimeter 42 of the flange portion 18 may be separated by a distance D when the removable membrane 28 is secured to a food container 10. More specifically, a reference circle 48 may be concentric with the outer perimeter edge 34 and have a diameter equal to a diameter of the outer perimeter edge 34, and a reference line 50 tangent to the reference circle 48 at the intersection of the reference circle 48 and the tab axis 44 may be separated from the forward edge 40 by a distance D. Preferably, the distance D may be any value between about 4 mm and about 10 mm, and, more preferably, the distance D may be about 7 mm. However, the distance D may be any suitable value for a particular application. In alternate examples, shown in FIG. 2B, a first rounded corner portion 52 may extend from a first end 54 of the forward edge 40 to a distal end 56 of the first lateral edge 36 and a second rounded corner portion 58 may extend from a second end 60 of the forward edge 40 to a distal end 62 of the second lateral edge 38.

In an alternative embodiment illustrated in FIG. 3A, the forward edge 40 may take the shape of an arc 64 such that the truncated tab portion 32 has the general shape of a truncated triangle having a slightly rounded forward edge. Put another way, the slightly rounded arc 64, the first lateral edge 36, and the second lateral edge 38 may collectively have the general shape of an upper portion (e.g., the upper three sides) of a trapezoid. More specifically, the slightly rounded arc 64, the first lateral edge 36, and the second lateral edge 38 may each correspond to a top side, an inwardly tapering first lateral side, and an inwardly tapering second lateral side, respectively, of a trapezoid that is wider at the base (i.e., a reference line that extends between the first and second lateral edges 36, 38 and that is parallel to an arc reference line 66 that is tangent to the arc 64 at a point intersecting the tab axis 44) and tapers towards the top (i.e., the arc 64). The arc 64 may have the shape of a segment of a circle, an oval, or a spline, for example. The arc 64 may be symmetrically disposed about the tab axis 44 such that the arc 64 is bisected by the tab axis 44, as illustrated in FIG. 3A. As shown in FIG. 3A, an arc reference line 66 that is tangent to the arc 64 at a point intersecting the tab axis 44 may form an oblique angle γ with each of the first and second lateral edges 36, 38. For example, the arc reference line 66 may form an angle γ between about 115 degrees and about 155 degrees with each of the first lateral edge 36 and the second lateral edge 38, and, preferably, the angle γ may be about 45 degrees. As illustrated in FIG. 3A, the arc reference line 66 and the outer perimeter 42 of the flange portion 18 may be separated by a distance D when the removable membrane 28 is secured to a food container 10. More specifically, a reference circle 48 may be concentric with and have a diameter equal to the outer perimeter edge 34, and a reference line 68 tangent to the reference circle 48 at the intersection of the reference circle 48 and the tab axis 44 may be separated from the arc reference line 66 by a distance D. Preferably, the distance D may be any value between about 4 mm and about 10 mm, such as about 7 mm, for example. However, the distance D may be any suitable value for a particular application.

In the embodiment illustrated in FIGS. 3A and 3B, the radius of curvature of the arc 64 (or the approximate radius of curvature if the arc 64 is not a circular segment) may be sufficiently large such that a first end 70 of the arc 64 non-tangentially intersects a distal end 56 of the first lateral edge 36 and a second end 72 of the arc 64 non-tangentially intersects a distal end 62 of the second lateral edge 38. More specifically, the arc 64 may have a radius of curvature greater than or equal to 75% of the radius of curvature of the circular outer perimeter edge 34. Preferably, the arc 64 may have a radius of curvature greater than or equal to the radius of curvature of the circular outer perimeter edge 34. In one embodiment, the arc 64 may intersect each of the first and second lateral edges 36, 38. In other embodiments, such as the embodiment illustrated in FIG. 3B, a first rounded corner portion 74 may extend from the first end 70 of the arc 64 to the distal end 56 of the first lateral edge 36 and a second rounded corner portion 76 may extend from the second end 72 of the arc 64 to the distal end 62 of the second lateral edge 38. In such an embodiment, a projection 78 of the first end 70 of the arc 64 (wherein the projection 78 extends along the general trajectory of the arc 64) non-tangentially intersects a projection 80 of the distal end 56 of the first lateral edge 36 (wherein the projection 80 extends along the general trajectory of the first lateral edge 36), and a projection 82 of the second end 72 of the arc 64 (wherein the projection 82 extends along the general trajectory of the arc 64) non-tangentially intersects a projection 84 of the distal end 62 of the second lateral edge 38 (wherein the projection 84 extends along the general trajectory of the second lateral edge 38).

In further alternative embodiments, the forward edge 40 may take the shape of plurality or a curved segments and/or linear segments that extend in a generally linear direction between the first lateral edge 36 and the second lateral edge 38. For example, as illustrated in FIG. 4A, the forward edge 40 may include a plurality of curved segments that cooperate to form a sinusoidal edge 86, and a reference line 88 may extend between the first lateral edge 36 and the second lateral edge 38 to bisect the sinusoidal edge 86. Put another way, the plurality of curved segments (comprising the sinusoidal edge 86) are arranged to collectively extend along the reference line 88 extending between the first lateral edge and second lateral edge 36, 38. The reference line 88 may intersect each of the first and second lateral edges 28, 30 to form an oblique angle, as described above. An additional example is shown in FIG. 4B, wherein the forward edge 40 includes a plurality of linear segments that cooperate to form a sawtooth-shaped edge 90. A reference line 92 may extend between the first lateral edge 36 and the second lateral edge 38 to bisect the sawtooth-shaped edge 90, and the reference line may intersect each of the first and second lateral edges 28, 30 to form an oblique angle, as described above. Put another way, the plurality of linear segments (comprising the sawtooth-shaped edge 90) are arranged to collectively extend along the reference line 92 extending between the first lateral edge and second lateral edge 36, 38. The reference lines 88, 92 discussed above and the outer perimeter 42 of the flange portion 18 may be separated by a distance D as described above. Preferably, the distance D may be any value between 4 mm and 10 mm, such as approximately 7 mm, for example. However, the distance D may be any suitable value for a particular application.

Configured as described above, the removable membrane 28 may be stacked and stored in a conventional magazine 14 for use in an automated process that seals the disposable food container 10. More specifically, as previously discussed and as illustrated in FIG. 2A, a conventional magazine 14 may have a plurality of vertical rods 16 (for example, six rods 16) that are disposed in the magazine 14 to be spaced around the perimeter of each of the removable membranes 12 in the stack stored in the magazine 14. The rods 16 are positioned to be in contact with or adjacent to portions of the perimeter of the membrane portion 30 (i.e., the outer perimeter edge 34) and the truncated tab portion 32 such that the plurality of rods 16 cooperate to prevent one or more removable membrane 28 from rotating relative to the stack of removable membranes 28. The plurality of rods 16 in the conventional magazine 14 may include a pair a forward rods 16 a, 16 b that are positioned adjacent to the distal ends of each of the first lateral edge 36 and the second lateral edge 38 when a stack of removable membranes 12 are disposed in the magazine 14. The plurality of rods 16 in the conventional magazine 14 may also include at least two rods 16 positioned to be in contact with or adjacent to portions of the outer perimeter edge 34. So configured, a stack of removable membranes 28 may be stored in conventional magazines 100 without the need to modify or in any way reconfigure the magazine 14, thereby avoiding extra costs associated with replacing and redesigning existing magazines 14.

Moreover, as briefly discussed above, the truncated tab removable membranes 28 require less material than membranes having conventional triangular tabs, thereby improving the overall aesthetic quality of the packaging and reducing the material cost. In addition, the above-described truncated tab design reduces the distance that the truncated tab portion 32 radially extends away from the membrane portion 30, thereby also reducing (or eliminating) the damage or undesirable interaction with secondary packaging caused by the conventional triangular tabs.

While various examples are described hereinabove as having forward edges 40 of different shapes, it should be appreciated that regardless of whether the forward edge 40 extends along a straight line, an arc, a sinusoidal shape, a sawtooth-shape, or otherwise, in each configuration the tab includes a profile that generally resembles a truncated triangle, which may otherwise be referred to as an upper portion of a trapezoid having converging sidewalls, for example, such as a tapered trapezoid. It is this shape that advantageously facilitates operation with the conventional magazine designs, increases aesthetic appeal, and minimizes damage to secondary packaging components.

While various embodiments have been described above, this disclosure is not intended to be limited thereto. Variations can be made to the disclosed embodiments that are still within the scope of the appended claims. 

1. A removable membrane for a disposable food container, the removable membrane comprising: a membrane portion, the membrane portion being at least partially defined by a circular outer perimeter edge; and a truncated tab portion projecting radially outward of the outer perimeter edge of the membrane portion, the truncated tab portion being at least partially defined by a first lateral edge and a second lateral edge, with each of the first lateral edge and the second lateral edge converging as the tab portion extends away from the outer perimeter edge of the membrane portion, the tab portion being further defined by a forward edge that extends along a straight line between the first lateral edge and second lateral edge, wherein the forward edge is disposed at an oblique angle relative to the first lateral edge and the second lateral edge.
 2. The removable membrane of claim 1, wherein the first lateral edge and the second lateral edge are symmetrically disposed about a tab axis that extends through a center point of the circular outer perimeter edge of the membrane portion.
 3. The removable membrane of claim 2, wherein a reference line tangent to a reference circle at the intersection of the reference circle and the tab axis is separated from the forward edge by a distance between about 4 mm and about 10 mm, and wherein the reference circle is concentric with the outer perimeter edge and has a diameter equal to a diameter of the outer perimeter edge.
 4. The removable membrane of claim 1, wherein a first rounded corner portion extends from a first end of the forward edge to a distal end of the first lateral edge and a second rounded corner portion extends from a second end of the forward edge to a distal end of the second lateral edge, and the linear edge portion of the forward edge extends between and is disposed between the first and second rounded corner portions.
 5. The removable membrane of claim 3, wherein each of the first lateral edge and the second lateral edge tangentially intersect the outer perimeter edge.
 6. The removable membrane of claim 1, wherein the forward edge forms an angle between about 115 degrees and about 155 degrees with the first lateral edge and the second lateral edge.
 7. The removable membrane of claim 1, wherein the forward edge is disposed at an angle of about 135 degrees relative to the first and second lateral edges.
 8. The removable membrane of claim 1, wherein the forward edge comprises a plurality of linear segments arranged to collectively extend along the straight line between the first lateral edge and second lateral edge.
 9. The removable membrane of claim 1, wherein the forward edge comprises a plurality of curved segments arranged to collectively extend along the straight line between the first lateral edge and second lateral edge.
 10. A removable membrane for a disposable food container, the removable membrane comprising: a membrane portion, the membrane portion being at least partially defined by an outer perimeter edge; and a truncated tab portion projecting radially outward of the outer perimeter edge of the membrane portion, the truncated tab portion being at least partially defined by a first lateral edge and a second lateral edge, with each of the first lateral edge and the second lateral edge converging as the tab portion extends away from the outer perimeter edge of the membrane portion, the tab portion being further defined by a forward edge that extends between the first lateral edge and the second lateral edge such that the forward edge, the first lateral edge, and the second lateral edge collectively have the shape of an upper portion of a trapezoid.
 11. The removable membrane of claim 10, wherein the forward edge extends along a straight line between the first and second lateral edges.
 12. The removable membrane of claim 11, wherein a reference line tangent to a reference circle at the intersection of the reference circle and the tab axis is separated from the forward edge by a distance between about 4 mm and about 10 mm, and wherein the outer perimeter edge has a circular shape and the reference circle is concentric with the outer perimeter edge and has a diameter equal to a diameter of the outer perimeter edge.
 13. The removable membrane of claim 10, wherein the forward edge is an arc.
 14. The removable membrane of claim 13, wherein the outer perimeter edge has a circular shape, and wherein the arc has a radius of curvature equal to or greater than a radius of curvature of the outer perimeter edge.
 15. The removable membrane of claim 13, wherein a first end of the arc non-tangentially intersects a distal end of the first lateral edge and a second end of the arc non-tangentially intersects a distal end of the second lateral edge.
 16. The removable membrane of claim 10, wherein the first lateral edge and the second lateral edge are symmetrically disposed about a tab axis that extends through a center point of the outer perimeter edge of the membrane portion.
 17. A system for storing a plurality of removable membranes for disposable food containers, the system comprising: a magazine having a plurality of vertical rods; and a plurality of removable membranes stored in the magazine, each removable membrane comprising: a membrane portion, the membrane portion being at least partially defined by an outer perimeter edge; and a tab portion projecting radially outward of the outer perimeter edge of the membrane portion, the truncated tab portion being at least partially defined by a first lateral edge and a second lateral edge, with each of the first lateral edge and the second lateral edge converging as the tab portion extends away from the outer perimeter edge of the membrane portion, the tab portion being further defined by a forward edge that extends between the first lateral edge and the second lateral edge such that the forward edge, the first lateral edge, and the second lateral edge collectively have the shape of an upper portion of a trapezoid, wherein at least two rods of the plurality of rods are adjacent to portions of the outer perimeter edge, at least one rod of the plurality of rods is adjacent to a distal end of the first lateral edge, and at least one rod of the plurality of rods is adjacent to a distal end of the second lateral edge, whereby the plurality of rods cooperate to prevent one or more removable membrane from rotating relative to the plurality of removable membranes stored in the magazine.
 18. The system of claim 17, wherein the forward edge extends along a straight line between the first and second lateral edges.
 19. The removable membrane of claim 18, wherein a reference line tangent to a reference circle at the intersection of the reference circle and the tab axis is separated from the forward edge by a distance between about 4 mm and about 10 mm, and wherein the outer perimeter edge has a circular shape and the reference circle is concentric with the outer perimeter edge and has a diameter equal to a diameter of the outer perimeter edge.
 20. The system of claim 17, wherein the forward edge is an arc. 